Personal computers have become so widely accepted that they now constitute a significant draw on the national power grid. For example, the computers in a large office building may consume more energy than the building's heating or lighting systems. As a result, attention has been directed toward improving personal computers so that they consume less energy. For example, a personal computer may have a reduced-power mode often called a “sleep mode.”
When the computer is idle for a predetermined period of time, as indicated by a control signal generated in the absence of activity from its keyboard, mouse, or other input device, the computer enters the sleep mode. When a user subsequently interacts with the computer, for example by moving the mouse, the computer awakens from the sleep mode and returns to its normal, full-power state of operation. Sleep mode is described in more detail in the following U.S. Pat. No. 6,268,845 to Pariza; U.S. Pat. No. 6,016,548 to Nakamura; U.S. Pat. No. 5,987,613 to Busch; and U.S. Pat. No. 5,721,935 to DeSchepper.
The need to awaken a personal computer from sleep mode can be an inconvenience to the user of the computer, as the computer may take a relatively long time to make the transition from asleep to awake. This can be especially annoying when the computer enters sleep mode when the user pauses only briefly for thought or conversation.
Consequently, a user of a personal computer often configures the personal computer to enter sleep mode only after it has been idle for a considerable time. For example, a personal computer may routinely continue to operate in full-power mode for twenty minutes or more after the user has left the office and therefore left the computer unattended. Thus, the desire for convenience may at times be fundamentally at odds with the need to conserve energy.
Battery powered personal computers, such as laptop computers, personal digital assistants, electronic notebooks, and the like may also have sleep modes. The purpose of having a sleep mode in a battery-powered device is to delay for as long as possible the need to recharge or replace the device's battery. Nevertheless, the same conflict between conservation and convenience applies also to personal computers that are powered by batteries, as battery-powered devices should enter sleep mode at the earliest convenient opportunity, in order to conserve battery life, and yet not inconvenience the user by entering sleep mode at an inopportune time.
As a result of the fundamental conflict between the desire to conserve energy and the desire not to inconvenience the user of a personal computer, there is a need to improve the operation of sleep mode for personal computers, so that a computer may enter sleep mode at the earliest convenient moment, and yet not needlessly inconvenience its user.